Can coating enamel



amn Feb. 2, 193? UNITED STATES CAN COATING ENAMEL Lehman E. Boag,Bellwood, 111., minor to American Can Company, New York, N. Y., acorporation of New Jersey No Drawing. Application October 24, 1933,Serial No. 695,041

4 Claims.

The present invention relates to coating materials and has particularreference to a process for preventing spangling and discoloration of theinterior of metallic containers for food products and also forpreventing discoloration of the container coating as well asdiscoloration of the contents of the can through the use of a moreuniversal coating of the baking enamel class applied to the can wall.The term spangling as understood in the can making industry is to anextent somewhat synonymous with the term discoloration". Specificallythe term spangling has reference to the discoloration of the tin platewhich follows in shape the etch figure of the tin crystals. Whereas theterm discoloration has specific reference to the dark areas more or lessgenerally distributed over areas of the surface of the plate, the termspangling" refers to the discoloration that follows the etch figure ofthe tin crystals.

Prior to the instant invention tin cans have been generally providedwith protective coatings for the packaging of food products to preventundesirable reaction between the metal or metals of the can and thepackaged materials, and these coatings have included resin, andsynthetic resin varnishes and enamels.

Some of these enamels have served as a protection against the action ofcertain food products. Other special coatings have been used to preventspangling and, or, discoloration of the can walls by certain less acidfood products, com for example, where the enamel has been pigmented withzinc or other oxides. The value, however, of these enamels as protectivecoatings has been restricted and special coatings have been foundnecessary for special products.

The present invention contemplates improvement in coatings of thischaracter to the end that a more universal use is possible so that asingle coating will serve more purposes and its value will be extendedto a larger range of products. Furthermore, the metal of the can is moreperfectly and fully protected against chemical reaction with the foodproducts and the coating itself is better able to withstand attack fromthe can contents before, during, and after processing of the product.

The improved coating is also easily made and applied and ordinaryvarnish manufacture and ordinary coating andbaking procedure of theenamels are in large part used. Viscosity is also easily controlledparticularly at the coating stage where the surfaces of the can or thosesurfaces which eventually form the inner can walls, are

covered with the enamel coat. This is important for much trouble hasbeen experienced in the past in the livering and thickening of somecoatings such as the zinc oxide group of special enamels, a thickeningaction being at times so great as to result in great losses of materialswhich must be discarded as unfit for use. In other cases, particularlywith the zinc oxide enamels, leaching of the zinc into the product islikely to occur and undesirable color effects are produced either on theproduct or the enamel.

The accomplishment of these desirable ends and the avoidance of theundesirable features in accordance with the instant invention areeffected by incorporating into the varnish or enamel a metallic soapwhich, unlike the zinc oxide previously used in the coatings mentioned,goes into solution in the enamels and provides substantially apermanently embodied material which does not react detrimentally withthe product to impair the coating, nor to spangle the can walls nor toaffect the product itself. Spotting or streaking and discoloration ofthe can wall or discoloration of coating or discoloration or impairmentof the product does not take place.

The metallic soap referred to may be incorporated with most of the resinvarnishes generally employed for the lining or coating of cans. Atypical varnish or vehicle for the-soap, as one example, may consist ofI rosin, copal gums, heat treated China wood oil, manganese resinate,and mineral spirits properly compounded.

The metallic soaps may take many forms of organo metallic compounds,organic compounds of zinc being preferred as far as present practicesare concerned. Magnesium, calcium, and other soaps may also be used. Theorgano zinc compounds in turn may be zinc linoleate, zinc tungate, zincresinate, zinc oleate, etc. The exact manner of making the soap isimmaterial to the present invention. As one example, a zinc linoleatemay be produced by the kettle method by heating the fatty acids oflinseed oil at a temperative of 450 F. and reacting with an equivalentweight of zinc oxide. The fatty acids of many drying and semi-dryingoils may be successfully used in such soap production.

The addition of the metallic soap to the enamel may be made in severalways during or after thinning of the enamel, a certain regard for thetemperatures being the only limitation. A more favorable way ofproceeding, however, is to first thin the zinc soap by an appropriatevarnish thinner which may comprise any one of a number of mineralspirits, and toluene has also been found to be very satisfactory. A soapsolution is thus obtained. This solution-will keep for a reasonable timeand may be added directly to the enamel without heating whenever mostconvenient, this usually being when the' enamel is to be run in thefactory. The standard practice in this regard is coating of the sheet inthe 1 flat and before fabrication into a can, so that baking of theapplied coating is thus most conveniently made. This is standard canmanufacture and further description for the instant purpose isunnecessary.

The metallic soap being neutral stable and permanent coating whenapplied to the interior walls of the can. It will not liver or thickenwhen applied by the usual coating rollers. It may be stored and usedonly as needed, this obviating any losses by deterioration.

It is thought that' the invention and many of its attendant advantageswill be understood from the foregoing description, and it will beapparent that various changes may be made inthe steps of the processdescribed and their order of accomplishment without departing from thespirit and scope of the invention or sacrificing all oi its materialadvantages, the process hereinbefore described being merely a preferredembodiment thereof.

I claim:

1. The process of preventing spangling oi the provides a enamel coatingfor the cans which contains a zinc tungate soapsoluble in the enamel.

3. The process of preventing spangling and discoloration of the interiorof metallic containers by the action of food products sealed in the canswhich comprises, providing a lacquer enamel coating for the cans whichcontains a zinc oleate soap soluble in the enamel.

4. The process of preventing spangling and discoloration of the interioroi. metallic containers by the action of food products sealed in thecans which consists in providing a lacquer enamel coating for the cans,said lacquer including'an organic metallic compound produced by chemicalreaction between 'zinc oxides and the fatty acids of the semi-dryingoils, said metallic compound being soluble-within the said lacquerenamel constitutingthe vehicle.

LEHNIAN E. HOAG.

